Ketje is an authenticated encryption scheme based on Keccak-p. It takes as input a secret key and a nonce, then some associated data (or metadata) that are authenticated but not encrypted and finally some plaintext. It produces a cryptogram comprising the ciphertext and a tag authenticating both the metadata and the plaintext. The recipient holding the same secret key can decrypt the cryptogram and check whether it is authentic.

Ketje supports also the concept of sessions. Without having to input the key again and a new nonce, the communicating parties can keep on exchanging metadata-plaintext pairs. Each time, the tag authenticates the complete exchange of messages so far.

Ketje Jr and Ketje Sr aim at compact implementations in constrained environments, whereas Ketje Minor and Ketje Major are research ciphers that aim at high speed.